Generally, this invention relates to balloon catheters. More specifically, this invention relates to balloon catheters used for stent delivery. Most specifically, this invention relates to balloon catheters useful for delivering bifurcated stents. In particular, this invention relates to balloon catheters, which deliver stents to an arterial bifurcation.
A stent is commonly used as a tubular structure left inside the lumen of a duct to relieve an obstruction. Commonly, stents are inserted into the lumen in a non expanded form and are then expanded autonomously (or with the aid of a second device in situ. A typical method of expansion occurs through the use of a catheter mounted angioplasty balloon which is inflated within the stenosed vessel or body passageway in order to shear and disrupt the obstructions associated with the wall components of the vessel and to obtain an enlarged lumen.
In the absence of a stent, restenosis may occur as a result of elastic recoil of the stenotic lesion. Although a number of stent designs have been reported, these designs have suffered from a number of limitations. These include restrictions on the dimension of the stent such as describes a stent which has rigid ends (8 mm) and a flexible median part of 7-21 mm. This device is formed of multiple parts and is not continuously flexible along the longitudinal axis. Other stent designs with rigid segments and flexible segments have also been described.
Other stents are described as longitudinally flexible but consist of a plurality of cylindrical elements connected by flexible members. This design has at least one important disadvantage, for example, according to this design, protruding edges occur when the stent is flexed around a curve raising the possibility of inadvertent retention of the stent on plaque deposited on arterial walls. This may cause the stent to embolize or more out of position and further cause damage to the interior lining of healthy vessels. (See FIG. 1(a) below).
Thus, stents known in the art, which may be expanded by balloon angioplasty, generally compromise axial flexibility to permit expansion and provide overall structural integrity.
Catheter balloons and medical devices incorporating them are well known for use in the surgical arena. For instance, during angioplasty, stenoses and/or obstructions in blood vessels and other body passageways are altered, in order to increase blood flow through the obstructed area of the blood vessel. For example, in a typical balloon angioplasty procedure, a partially occluded lumen is enlarged through the use of a balloon catheter that is passed percutaneously by way of the arterial system by way to the site of the vascular obstruction. The balloon is then deflated to dilate the vessel lumen at the site of the obstruction.
Furthermore, another typical procedure uses a xe2x80x9cscaffolding,xe2x80x9d or stent placed on the balloon angioplasty catheter for similar delivery through the arterial system to the site of a vascular obstruction. Thereafter, the balloon angioplasty catheter is inflated, thereby expanding the stent placed on the catheter. When the stent expands, it similarly expands the lumen so that after removal of the deflated catheter, the stent is retained in its expanded position and thereby holds open that formerly obstructed area of the body passageway.
Essentially, a balloon catheter is a thin, flexible length of tubing having a small inflatable balloon at a desired location along its length such as at or near its tip. Balloon catheters are designed to be inserted into a body passageway such as the lumen of a blood vessel, a passageway in the heart, a urological passageway, and the like. Typically, the passage of the balloon catheter into the body passageway is done with guidance, such as x-ray or fluoroscopic guidance.
In practice, stent delivery is quite complex. That is, a stent is sometimes required to be placed in a rather tortuous area of the vasculature. In this instance, it is often necessary to have a catheter which is capable of negotiating tight turns, and/or being placed along a bifurcated length of blood vessel. In some instances, while a generally occluded section of blood vessel can readily be stented, it is often difficult to place a second stent at the other portion of a bifurcation. In other words, one can imagine the bifurcation as an inverted letter xe2x80x9cYxe2x80x9d within the body. (The approach of the catheter concerning this inverted xe2x80x9cYxe2x80x9d shape is generally through one of the legs in the xe2x80x9cYxe2x80x9d.) Therefore, the balloon passes both between the leg and the trunk or base of the xe2x80x9cYxe2x80x9d rather readily. However, once a stent is placed along these two legs, it is rather difficult to place a second stent at or near the junction of the first leg and the base of the letter xe2x80x9cYxe2x80x9d. Of course, the same can hold true when the approach is via the base of the xe2x80x9cYxe2x80x9d and delivery of the first stent is to one of the legs. This is all the more true because as one advances through the vasculature, the arterial sizes go from quite large (greater than 1 cm diameter) to rather small (some time less than 2.5 mm diameter).
It would be desirable, therefore, to create a system which allows for delivery of a single stent or pair of stents at a bifurcation in the vasculature. It would further be desirable for this stent or for this delivery system to be able to negotiate the bends of the bifurcation, and moreover, to provide for easy access when one stent is already placed. Furthermore, it would be quite useful in order to be able to apply the second stent, for the first stent to be reliably placed every time so that the user knows exactly where the bifurcation is located, and as well where the stent must be appropriately oriented in order to readily access the second leg of the xe2x80x9cYxe2x80x9d of the bifurcation.
Finally, it would be useful for a device such as a desired delivery system to carry a stent capable of allowing secondary access to a bifurcated portion of the vasculature. Thus, it would be most desirable for the device to comprise a catheter capable of balloon delivery of a stent at a bifurcation, and also balloon delivery of a second stent at the bifurcation.
The present invention overcomes some perceived shortcomings of prior art stents by providing a stent with axial flexibility. In a preferred embodiment, the stent has a first end and a second end with an intermediate section between the two ends. The stent further has a longitudinal axis and comprises a plurality of longitudinally disposed bands, wherein each band defines a generally continuous wave along a line segment parallel to the longitudinal axis. A plurality of links maintains the bands in a tubular structure. In a further embodiment of the invention, each longitudinally disposed band of the stent is connected, at a plurality of periodic locations, by a short circumferential link to an adjacent band. The wave associated with each of the bands has approximately the same fundamental spatial frequency in the intermediate section, and the bands are so disposed that the waves associated with them are spatially aligned so as to be generally in phase with one another. The spatially aligned bands are connected, at a plurality of periodic locations, by a short circumferential link to an adjacent band.
In particular, at each one of a first group of common axial positions, there is a circumferential link between each of a first set of adjacent pairs of bands.
At each one of a second group of common axial positions, there is a circumferential link between each of a second set of adjacent rows of bands, wherein, along the longitudinal axis, a common axial position occurs alternately in the first group and in the second group, and the first and second sets are selected so that a given band is linked to a neighboring band at only one of the first and second groups of common axial positions.
In a preferred embodiment of the invention, the spatial frequency of the wave associated with each of the bands is decreased in a first end region lying proximate to the first end and in a second end region lying proximate to the second end, in comparison to the spatial frequency of the wave in the intermediate section. In a further embodiment of the invention, the spatial frequency of the bands in the first and second end regions is decreased by 20% compared with the spatial frequency of the bands in the intermediate section. The first end region may be located between the first end and a set of circumferential links lying closest to the first end and the second end region lies between the second end and a set of circumferential links lying closest to the second end. The widths of corresponding sections of the bands in these end regions, measured in a circumferential direction, are greater in the first and second end regions than in the intermediate section. Each band includes a terminus at each of the first and second ends and the adjacent pairs of bands are joined at their termini to form a closed loop.
In a further embodiment of the invention, a stent is provided that has first and second ends with an intermediate section therebetween, the stent further having a longitudinal axis and providing axial flexibility. This stent includes a plurality of longitudinally disposed bands, wherein each band defines a generally continuous wave having a spatial frequency along a line segment parallel to the longitudinal axis, the spatial frequency of the wave associated with each of the bands being decreased in a first end region lying proximate to the first end and in a second end region lying proximate to the second end, in comparison to the spatial frequency of the wave in the intermediate section; and a plurality of links for maintaining the bands in a tubular structure. The first and second regions have been further defined as the region that lies between the first and second ends and a set of circumferential links lying closest to the first end and second end.
In a further embodiment the widths of the sectionals of the bands, measured in a circumferential direction, are greater in the first and second end regions than in the intermediate section.
In yet an additional embodiment, the stent is divided into a group of segments, and each of the segments are connected by a flexible connector. In addition, the stent segments are provided with enhanced flexibility at the flexible connectors, due to the geometrical configuration of the flexible connectors.
Furthermore, the current stent can be modified to provide for bifurcated access, whereas the stent itself is uniform throughout. If the manufacturer designs such a stent to have an essential opening, then it is possible to place the stent such that a pair of stents can be placed one through the other. In this fashion, the stents are capable of being placed at a bifurcation, without any welding or any special attachments. The interlocking mechanism can be incorporated into the stent design to cause the stent to interlock at the desired position during assembly of the device.
In practice, therefore, the current catheter device consists of a balloon catheter which comprises a shaft portion having a proximal and a distal end. The shaft portion has a guidewire lumen therethrough. The lumen has a proximal opening and a distal opening. The distal opening of the shaft portion is located at the distal end of the shaft. A balloon is connected to the shaft at the shaft distal end. The balloon has proximal and distal ends and a first guidewire lumen through it. The balloon guidewire is in fluid communication with the guidewire lumen of the shaft and the first balloon guidewire lumen also has proximal and distal ends. The balloon has a second guidewire lumen, the second guidewire lumen containing a distal opening located proximal to the distal opening of the first guidewire lumen.
Further, there is disclosed a method of stent placement which comprises first guiding a guidewire through the vasculature. Second, a balloon catheter which contains two guidewire lumens is strung along the guidewire into position at the bifurcation. The distal opening of the second guidewire lumen abuts the proximal end of the bifurcation. Thereafter, a second guidewire is strung through the first balloon catheter and out the distal opening of the second guidewire lumen. Thus, resident in the second bifurcation leg is the second guidewire. Then, a second standard stent delivery balloon catheter is guided along the second guidewire to a position within the bifurcation. Typically, expansion of both stents can be done one right after the other after proper placement of the first and second balloons.